This invention relates generally to the handling of dry bulk materials and more particularly to a knife gate valve which is specially constructed to clear particulate matter from the gate and sealing surfaces during open and closing movement of the gate.
The handling of various types of dry bulk materials frequently involves conveying of the material by means of a pneumatic or vacuum conveying system. Among the types of solid particulate materials that are handled in this fashion are powdered materials and granular materials such as foods, grain and plastics. The conveying system typically includes flow control devices that may be knife gate valves, butterfly valves or rotary air locks.
Although knife gate valves are widely used in this type of application, the knife gates that have been available in the past have not been wholly free of problems. Perhaps the most prevalent problem has been the tendency for particulate matter to become wedged inside of the valve, usually between the gate and its sealing surfaces. This can cause the gate to bind or otherwise operate unsatisfactorily, and it can also impair the sealing action and cause leakage of air or vacuum. The particulate matter can also build up on the gate or other internal surfaces and cause similar problems. Valves that are intended for controlling the flow of fluids are ineffective when they must be closed in the presence of a stream of particulate material flow. Another problem with prior valves has resulted from the use of soft rubber seals which are susceptible to erosion and other deterioration caused by the abrasive action of the particulate material.
Accordingly, a need remains for a gate valve which can be effectively closed and sealed in the presence of particulate flow and which is constructed to operate effectively for extended periods of service.
The present invention is directed to a gate valve which provides a positive seal across the valve opening in the presence of a stream of material flow. The valve utilizes dynamically loaded, hard polymer seals which promote wear resistance and long term trouble free service. These gate seals provide positive material and air shut off to present a dust tight valve operation in pneumatic and vacuum conveying systems. The course of the gate between its open and closed positions is defined by a pair of dynamically loaded guide bars. The leading edge of the gate clears the material on these track-like guide bars during closure so as to present a self-cleaning action. Transverse gate seals that extend along opposed surfaces of the gate seal effectively and are easily lubricated and/or air purged. The lubricating seals extend gate life in severe service applications. These transverse seals are easily accessible for inspection or replacement without removal of the gate valve from service, so production down time is minimized. Seals along the top and bottom surfaces of the gate further seal the gate and clean the internal surfaces of particulate matter as the gate opens and closes.
It is therefore a general object of this invention to provide a gate valve which is constructed to effectively seal both particulate solids and differential air pressures between conduits upstream and downstream.
Another object of this invention is to provide a gate valve which keeps the interior seals free from particulates so as to enhance the sealing capabilities and minimize the seizing and binding of the gate during use.
A still further object of this invention is to provide a gate valve of the character described which utilizes dynamically loaded hard polymer seals so as to extend the seal life and promote trouble free service.
Another important object of this invention is to provide a gate valve which is constructed in a manner to keep the gate free of particulates.
A further object of this invention is to provide a gate valve of the character described which makes use of dynamically loaded guide bars along the side edges of the gate in order to enhance the reciprocative gate movement between open and closed positions. The guide bars are arranged to avoid the wedging of particulate matter along the sides of the gate, thus promoting extended service of the seals.
Another particular object of this invention is to provide a gate valve of the character described which precludes internal material buildup so as to eliminate gate seizing and binding.
A still further object of this invention is to provide a gate valve which is interchangeable with various releasably-connected actuators so as to preclude the need to remove the gate valve from use during service.
Another object of this invention is to provide a gate valve in which the external air seals are readily accessible for inspection or replacement while the valve remains in service.
An additional object of the invention is to provide a gate valve of the character described which is equipped with multiple sets of external air seals and with fluid ports leading to channels between the seals in each set so that each seal can be lubricated and/or purged by the application of air under pressure.